The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to an improved wiring structure in a semiconductor device and a manufacturing method thereof.
In a semiconductor device, a tungsten silicide film or a titanium silicide film is used as an electrode material or an interconnection material.
For example, FIG. 6 shows a structure of a MOS transistor. A pair of high concentration impurity regions la are formed on a silicon substrate 1. A gate oxide film 2 is formed on a channel region 1b sandwiched between the impurity regions 1a, and a gate electrode is further formed thereon. Employed as the gate electrode is a two-layered film structure which consists of an impurity-containing polysilicon film 3 and a silicide film 5 (the tungsten silicide film or the titanium silicide film) formed on the polysilicon film 3.
Also, employed in FIG. 7, for example, as a wiring structure for making contact with a silicon substrate 1 is a two-layered film structure which, in much the same way as in FIG. 6, consists of a polysilicon film 3 and a silicide film 5 formed on the polysilicon film 3.
When such a two-layered film structure undergoes a high temperature heat treatment at about 800xc2x0 C., and if the two-layered film interface is of an unstable structure, then silicon in the polysilicon film or the silicide film aggregates at the interface, which bring about a discontinuity of the film in quality and the thickness. As a result, the problems will arise such as an increase in wiring resistance or a patterning irregularity.
For instance, Japanese Patent Laid-Open No. Hei 8-250727 discloses a method for solving such problems, in which, as shown in FIG. 8, a titanium oxide-containing titanium silicide film 5a is interposed between a polysilicon film 3 and a titanium silicide film 5. Formation of the titanium oxide-containing titanium silicide film 5a has been described as follows. First, in an oxidizing atmosphere, a heat treatment of the polysilicon film 3 oxidizes the surface thereof. Then, a thermal reaction is carried out between the oxidized surface and the titanium silicide film 5 formed thereon, thus the titanium oxide-containing titanium silicide film 5a is formed.
Japanese Patent Laid-Open No. Hei 1-287963 discloses a method in which a metal oxide film is interposed between a polysilicon film and a silicide film. The processing steps are shown in FIG. 9, and formation of the metal oxide film has been described as follows. First, a gate oxide film 2 is formed on a silicon substrate 1 (FIG. 9(a)). Second, by leaving in an atmosphere a polysilicon film 3 formed thereon, a natural oxide film 7 is formed on the surface thereof (FIG. 9(b)). Then, a metal 8 (for example Ti), which has higher oxidation reaction heat than the silicon oxide film, is thinly formed, and a silicide film 5 is formed thereon further (FIG. 9(c)). Finally, by heat treatment, a reaction will occur between the natural oxide film 7 and the metal film 8, and a metal oxide film 10 (TiOx) is formed at the interface between the polysilicon film and the silicide film (FIG. 9(d)). It is shown that the patterning thereof is made thereafter (FIG. 9(e)).
In both of the prior art, a thin oxide film is, first of all, formed on a polysilicon film surface. A method of forming the oxide film is classified into a method of performing a heat treatment in an oxidizing atmosphere and a method of leaving in an atmosphere. The former finds it difficult to uniformly form a relatively thin film, and at the same time has a problem of increasing the number of the processing steps. Also, the latter takes a time to form a certain quantity of oxide film and finds it difficult to control a thickness of the oxide film, and what is more, gives rise to a worry about contamination from the atmosphere.
The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a method of forming, easily and with an excellent controllability, a thin and clean oxide film on a polysilicon film surface in order to form a stable interface in a two-layered film structure which consists of a polysilicon film and a silicide film formed thereon.
Furthermore, the present invention not only makes it possible to form a conduction film of stable characteristics but also provides a semiconductor device in which the conduction film is used and a manufacturing method thereof.
According to one aspect of the present invention, in a method of manufacturing a semiconductor device, a silicon film is formed in a semiconductor wafer. A thin film of a silicon oxide is formed on the silicon film by means of a treatment with an oxidizing chemical. A silicide film is formed on the thin film of the silicon oxide.
Further, in the method, after the silicon film is formed but before the thin film of the silicon oxide film is formed, an oxide film formed naturally on a surface of the silicon film is removed.
In the method, the oxidizing chemical is preferably one kind of oxidizing chemical, a mixed chemical of two kinds or more of oxidizing chemicals, or a mixed chemical of an oxidizing chemical and a non-oxidizing chemical.
In the method, the one kind of oxidizing chemical is preferably a sulfuric acid solution, a nitric acid solution, a hydrogen peroxide, or an ozone water.
In the method, the mixed chemical of two kinds or more of oxidizing chemicals is preferably a mixed chemical of a sulfuric acid solution and a hydrogen peroxide, or a mixed chemical of a sulfuric acid solution and an ozone water.
In the method, the mixed chemical of an oxidizing chemical and a non-oxidizing chemical is preferably a mixed chemical of a hydrogen peroxide and a hydrochloric acid solution or an ammonia solution, or a mixed chemical of an ozone water and a hydrochloric acid solution or an ammonia solution.
In the method, the thin film of the silicon oxide film is preferably formed to be 200 xc3x85 or less in thickness.
Other and further objects, features and advantages of the invention will appear more fully from the following description.